1. Field of the Invention
The present invention relates to a telephone exchange system and A switching connection method for performing a switching connection among telephones and various kinds of exchanges in a telephone line, and more particularly to a telephone exchange system and its switching connection method capable of performing an efficient switching connection when successively making calls on a plurality of telephones having an identical out-of-town telephone exchange.
2. Description of the Related Art
The description will be made in the case where a predetermined subscriber successively phones a plurality of subscribers of an out-of-town exchange other than the sending party's out-of-town exchange, by use of the conventional exchange system, on a telephone line. As illustrated in FIG. 7, assume that a subscriber (A) having a telephone 71 successively makes a call to a subscriber (B) having a telephone 72, a subscriber (C) having a telephone 73, and a subscriber (D) having a telephone 74.
With reference to FIG. 7, the telephone 71 is accommodated in a local exchange (LS-A) 75 and the local exchange 75 is connected to an out-of-town exchange (TS-A) 76. The telephone 72 is accommodated in a local exchange (LS-B)77, the telephone 73 is accommodated in a local exchange (LS-C)78, and the telephone 74 is accommodated in a local-exchange (LS-D) 79, respectively. The local exchanges 77, 78 and 79 are respectively connected to an out-of-town exchange (TS-B) 80. Further the out-of-town exchange 76 is connected to the out-of-town exchange 80.
In order to phone the subscriber (B), the subscriber (A) dials the telephone number of the telephone 72 from the own telephone 71, that is out-of-town exchange number+local exchange number+subscriber phone number (hereinafter, this combination is referred to as a national number). This establishes a call connection through the path 1, enabling communication between the telephones 71 and 72. After completion of the communication, the subscriber (A) dials the national number of the telephone 73 from the telephone 71 in order to call the subscriber (C). This establishes a call connection through the path 2, enabling communication between the telephones 71 and 73. Further, after completion of this communication, the subscriber (A) dials the national number of the telephone 74 from the telephone 71 in order to call the subscriber (D). This establishes a call connection through the path 3, enabling communication between the telephones 71 and 74.
The control operation of each exchange when performing each call connection as mentioned above will be described with reference to FIG. 8. If the telephone 71 is off the hook by the subscriber (A), the local exchange 75 detects the off-hook and transmits a dial tone (DT) to the telephone 71. The subscriber (A), upon confirmation of the dial tone, dials the corresponding national number of the telephone 72 by use of the dial button of the telephone 71. The local exchange 75, upon receipt of the dial signal from the telephone 71, transfers the dial signal to the out-of-town exchange 76, in order to transfer the dial signal to the out-of-town exchange 80 specified in the dial signal. The out-of-town exchange 76 transfers the dial signal to the out-of-town exchange 80 that is a corresponding exchange specified by the dial signal received from the local exchange 75. The out-of-town exchange 80 transfers the dial signal to the local exchange 77 corresponding to the local exchange number specified by the received dial signal. The local exchange 77 sends a call signal (RINGING) to the telephone 72 that is of the corresponding subscriber number specified by the received dial signal and sends a call tone (RGT) to the telephone 71.
Upon detection of the off-hook of the telephone 72, the local exchange 77 performs a call (communication channel) connection. This enables communication between the telephones 71 and 72. If the telephone 71 is on the hook, the local exchange 75 detects the on-hook of the telephone 71, a ring-off signal is transferred to the out-of-town exchange 76, the out-of-town exchange 80, and the local exchange 77 one after another, and the call is broken.
Each exchange performs the switching operation in the same procedure as the above, also in case of dialing from the telephone 71 to the telephone 73. The local exchange 78 performs the switching operation instead of the local exchange 77 in this case. Further, it is similar in case of dialing from the telephone 71 to the telephone 74. In this case, the local exchange 79 performs the switching operation instead of the local exchange 77.
As mentioned above, in the conventional telephone exchange system, it is necessary to dial each national number for every party when a telephone call is successively made to a plurality of subscribers existing in the identical area. Therefore, the connection is troublesome and time consuming.
In order to decrease the subscriber's trouble in dialing in every time of communication, it may be considered to use a dial shortening function and a redial function provided in a telephone. However, use of the dial shortening function is restricted to the case of calling the party having been registered beforehand, and the redial function is a function of dialing the same number of the party having been called last time. Therefore, it is not available in the above-mentioned case of calling each different party one after another. Though these functions can save the labor of a subscriber, they cannot shorten the time itself required for the switching connection, but they are only to dial the number instead of a subscriber.
The Japanese Patent Publication Laid-Open (Kokai) No. Heisei 1-168147 "Dialing Method by Exchange Difference in General Telephones" discloses a technique for shortening a dial operation by storing either an out-of-town exchange or a local exchange of the calling party when dialing a calling party, and when calling the same party later, automatically sending the stored out-of-town exchange or local exchange by a specified key operation. However, this technique cannot shorten the time required for a switching connection even if it can save the labor of a user.